Okay...I just got my car smogged today and I'm releaved to say that I passed....but just barely. This time the NOx reading at 15mph was 414ppm, the last reading was 443ppm with a maximum allowable of 419ppm. So I basically passed by 5ppm The tech had to retest the car 3 times before it would pass....while doing the first run he knew that it was having trouble, so he sped up the car passed the 15mph mark to force the smog computer to reset...he had to do this twice before it passed. Cool guy!!!!!

After the first inital smog test that I failed I seafoamed the car, changed the passenger side O2 sensor, fixed an exhaust leak, and changed the oil. In the process of yanking the exhaust manifold to fix the exhaust leak I busted a bolt in the head . So I just used a **** load of RTV and a new header gasket to seal it up...it leaks and ticks but seems to run okay with a minor miss however I'm still getting high NOx readings. Anyone have a clue what this may be? The car is a 97' Z28 with 72K on the clock...with OEM wires and plugs

I don't have to worry about a smog check for another 2 years....so the long tubes are going on this weekend heheheh.....

I would like to thank everyone that helped me in diagonsing this problem and lending me parts to get my car moving. I'll keep you guys updated on the Jet Hot long tube install.



-B

 

Congrats! I'm dreeding taking my test. I hate this crap.

 

You will probably get more responses in adv. tech, but I'll take a shot at it. NOx only comes into play when combustion chamber temps reach 2500+ F. The only reason that you would have an abnormally high amount of NOx would be, obviously, from a lean mixture. When is this high reading happening? You might what to replace your wires and plugs before you next smog test as a misfire can cause this problem. If you still have the problem after that I would start to look at the read out of sensors as that possibly could tell you a more deffinate answer.

 

I believe NOx has to do with high combustion temperatures. Something might be making it lean. It is difficult to say without looking at your BLMs.

 

We answered at the same time! Sorry, didn't mean to be redundant.

If you had an ignition misfire, you'd pass unburnt fuel into the exhaust forcing a rich condition. However, an injector issue that energizing intermittantly would be an issue by missing a pulse.

 

so do you have a blown 383 or is that just your sn.. kinda like mine turbo_Z but no turbo

 

The car is stock..no $$$ for a blown 383 yet.

-B

 

Something does not look right. My car with a cam (cc305), shorties, ported heads and stock tuning made 109 ppm and 135 ppm 1 year ago. The g/f car was tested last weekend (bone stock '97 with over 150k miles) and produced less than 100ppm at both speeds.

Is your car in a good state of tune?

 

There is 72K on the clock with stock plugs, wires, and opti. So I guess the answer would be "no"?

-B

 

Having an exhaust leak will mess up your 02's ability to function properly and may not allow the cat's to store oxygen as the engine goes from rich to lean keeping it within the 14.7 threshold on closed loop....

1. before you get it smoged again I would get that bolt drilled out and fixed.

2. If it sill fails you may also need some new cat(s) as the materials inside do ware out...I run dual 3"ID carsound cats which are not OBDII approved but at this time the BAR is not inforcing it much out here in CA and they are a three way cat....I've found a shop that sells them off the internet for $59.95 and these are the high flow models.


Ken